1. Field of the Invention
The present invention relates to a system and method for controlling the luminous output of gas discharge lamps over a very broad dynamic range and more particularly to a fluorescent lamp dimmer arrangement which varies the light intensity over a range from less than 1 ftL to over 10,000 ftL.
2. Problem to be Solved
At present, commercially-available dimmers for fluorescent lamps operate over a range of approximately 150:1 or only 46 dB. However, it is necessary and desirable to control the luminous output of fluorescent tubes over a very broad dynamic range in special applications, such as the backlighting of an LCD display in a military airborne environment where a range from approximately 10,000 ftL to about 1 ftL (80 dB) is required. Some lamp dimmer circuits developed in the aerospace industry have improved the commercial performance with dimming ratios approaching 2000:1 or 66 dB. Achieving operation and control of lamp luminosity over a still greater and required range of 10,000:1 or more is not straightforward due to the nature of the fluorescence phenomenon.
In order to understand how to control the luminous output of a fluorescent lamp, it is necessary to fully understand how they operate, their basic limitation, and most importantly the nature of their electrical characteristics that determine the "load" that the fluorescent lamp will present to the lamp driving circuits.